| Computer Code: |
STIE |
Preferred Map Code: |
notEntered |
| Status Code: |
Full |
| Age range: |
Early Devonian Epoch (DL)
— Early Devonian Epoch (DL) |
| Lithological Description: |
The Struie Formation is largely composed of grey or reddish brown, micaceous siltstone and mudstone, with only occasional thin beds of very fine-grained, greyish brown, silty, calcareous sandstone (Richards, 1990). These sediments include highly radioactive horizons that are likely to be organic-rich partings. They also include occasional laminations of black mudstone, microcrystalline dolomite, and micritic limestone. The siltstones are commonly rippled, and Richards (1985) identified small slump structures in core from 12/27-1. The siltstones and mudstones overlie a basal Devonian quartzite at 12/29-2, comprising grey and pink pseudomorphic quartz grains cemented by calcite and dolomite. Beds of conglomerate are interbedded within a 68 m siltstone section in the middle of the Struie Formation in well 12/28-2; the conglomerate comprises pebbles of igneous and metamorphic basement in a very fine to very coarse grained sandy matrix. |
| Definition of Lower Boundary: |
The Struie Formation rests on metamorphic or granitic basement in all sections. |
| Definition of Upper Boundary: |
The top of the Lower Old Red Sandstone is an angular unconformity throughout Scotland (Mykura, 1991), except at the centre of the Orcadian Basin, where there is a conformable transition to Middle Old Red Sandstone. In southern Quadrant 12, the Struie Formation is overlain by Middle Devonian alluvial-fan sandstones and conglomerates or by Permian sediments. In well 13/19-1, lacustrine Lower Devonian sediments are overlain by fluvial Middle Devonian deposits, and the boundary is defined by a sharp downhole increase in gamma-ray response, velocity and resistivity, and by a change in dipmeter response. |
| Thickness: |
A complete, 521 m-thick Lower Devonian section was encountered in well 12/29-2, whereas the sediments are at least 976 m thick in nearby well 12/27-1. Equivalent sediments are 2400 m thick along strike in Ross and Cromarty (Armstrong, 1977). |
| Geographical Limits: |
Inner Moray Firth occurrences of Lower Devonian sediments are restricted to southern Quadrant 12 and well 13/19-1. They were deposited either in a single, large intermontane basin or in two separate basins on the hanging walls of the Smith Bank and Lossiemouth faults, respectively. |
| Parent Unit: |
Lower Old Red Group (LOOR)
|
| Previous Name(s): |
Struie Group [Obsolete Name And Code: See STIE]
(STRU)
|
| Alternative Name(s): |
none recorded or not applicable
|
| Stratotypes: |
| Reference Section |
North Sea well 12/27- 1: 2345-3323.5 m TD (7693-10904 ft TD) below KB (Cameron, 1993). |
| Reference Section |
North Sea well 12/29- 2: 2972-3508 m (9750-11510 ft) (Cameron, 1993). |
| Reference Section |
North Sea well 13/19- 1: 1987-2153 m TD (6518-7064 ft TD) (Cameron, 1993). |
| Reference(s): |
| Armstrong, M. 1977. The Old Red Sandstone of Easter Ross and the Black Isle. In Gill, G (editor). The Moray Firth area - geological studies. Inverness Field Club. |
| Mykura, W. 1991. Old Red Sandstone. 297-346 in Geology of Scotland (3rd edition, revised). Craig, G Y (editor). Geological Society of London. |
| Richards, P C. 1985. A Lower Old Red Sandstone lake in the offshore Orcadian basin. Scottish Journal of Geology 21, 381-383. |
| Andrews, I J, Long, D, Richards, P C, Thomson, A R, Brown, S, Chesher, J A, and McCormac, M. 1990. The geology of the Moray Firth. (London: British Geological Survey.) |
| Norton, M G, McClay, K R, and Way, N A. 1987. Tectonic evolution of Devonian basins in northern Scotland and southern Norway. Norsk Geologisk Tidsskrift 67, 323-338. |
| Sweet, I P. 1985. Sedimentology of the Lower Old Red Sandstone near New Aberdour, Grampian Region. Scottish Journal of Geology 21, 239-259. |
| Waters, C N, Gillespie, M R, Smith, K, Auton, C A, Floyd, J D, Leslie, A G, Millward, D, Mitchell, W I, McMillan, A A, Stone, P, Barron, A J M, Dean, M T, Hopson, P M, Krabbendam, M, Browne, M A E, Stephenson, D, Akhurst, M C, and Barnes, R P. 2007. Stratigraphical Chart of the United Kingdom: Northern Britain. (British Geological Survey.) |
| Cameron, T D J. 1993. 4. Triassic, Permian and pre-Permian of the Central and Northern North Sea. In: Knox, R W O'B and Cordey, W G (eds.) Lithostratigraphic nomenclature of the UK North Sea. British Geological Survey, Nottingham. |
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: |
|
S073
S073
S108
|
